Flow Instability in a Parallel Channel Loop Under Two-Phase Natural Circulation
Vikas Jaina, A. K. Nayakb, P. K. Vijayanc, D. Sahad and R. K. Sinhae
Reactor Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 095, India.
ajainv@barc.gov.in
barunths@barc.gov.in
cvijayanp@barc.gov.in
ddsaha@barc.gov.in
erksinha@barc.gov.in
ABSTRACT
Natural circulation systems under two-phase flow conditions are susceptible to various kinds of instabilities. Density wave instability is the most commonly encountered instability in two-phase boiling systems. With parallel channels connected between common plena, this instability may assume many different modes like in-phase, out-of-phase or mixed mode oscillations. The complex oscillation modes of boiling parallel channels under equally as well as unequally heated condition particularly at low pressures are a subject of investigation because of their relevance to natural circulation based Boiling Water Reactors. To investigate such behavior an experimental facility ‘Parallel Channel Loop’ (PCL) with four parallel and nearly identical channels has been setup. Experiments are conducted over wide range of pressures and channel powers. Experimental investigations encompass the transition through various regimes such as single-phase to two-phase and unstable to stable flow conditions. Flow oscillations under certain conditions are found to have complex characteristic as the oscillatory behavior is aperiodic and characterized by varying frequency and amplitude of oscillations. These aperiodic oscillations are further complicated by varying phase difference among the channels. Instability behavior of channel flow is studied in terms of the evolution of oscillatory flow among the channels. The effects of pressure and power on instability are also studied.
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